Glow plug

ABSTRACT

The invention relates to a glow plug comprising a housing ( 1 ), a glow element ( 2 ) which extends out of the housing ( 1 ), a supply lead ( 4 ) which is connected to the glow element ( 2 ) via a contact spring ( 5 ) and is enclosed by the housing ( 1 ). According to the invention, the contact spring ( 5 ) is a sleeve having at least one slit ( 6 ) extending transversely to the longitudinal direction of the sleeve.

DESCRIPTION

The invention is directed to a glow plug having the features in the preamble of claim 1.

To transfer current and compensate for motions of the glow element, glow plugs can be equipped with a contact spring via which the glow element is connected to a supply lead.

The problem addressed by the invention is that of demonstrating a way in which glow plugs can be manufactured with less expenditure.

This problem is solved by a glow plug having the features indicated in claim 1. Advantageous developments of the invention are the subject matter of dependent claims.

According to the invention, a sleeve having at least one slit extending transversely to the longitudinal direction of the sleeve is used as a contact spring. Assembly is advantageously simplified in this manner. Namely, a sleeve can be easily oriented coaxially with the glow element and the supply lead e.g. by being inserted thereon. Tilting that would occur during outward spring deflection is easily prevented. The contact spring can be fastened to the glow element and the supply lead easily e.g. by welding, soldering, or crimping.

Advantageously the spring hardness of the contact spring according to the invention can be adapted to the requirements of a given type of glow plug by the number of slits. Without changing the installation techniques, the spring hardness can therefore be designed precisely as needed and can be matched to the installation space of a glow plug type.

Preferably the at least one slit extends perpendicularly to the longitudinal direction of the sleeve. A resilient extensibility or tractility of the sleeve in the longitudinal direction can also be attained by one or more slits extending obliquely to the longitudinal direction. The depth of the slit or slits is preferably greater than half of the outer diameter of the sleeve. If the slit depths are shallower, the deformability of the sleeve in the longitudinal direction is improved only slightly. Slit depths greater than two-thirds, in particular greater than three-fourths of the outer diameter of the sleeve are particularly preferred. Slit depths between one-tenth and one-fifth of the outer diameter of the sleeve are advantageous in particular. The depth of a slit is understood to mean the extension thereof perpendicularly to the longitudinal direction of the sleeve.

The maximum possible compression of the spring is determined by the width of the slit or slits. Slit widths between one-tenth and one-fourth of the outer diameter of the sleeve, and, in particular, between one-seventh and one-fourth of the outer diameter of the sleeve are particularly advantageous.

According to an advantageous development of the invention, at least two slits are provided, which are interspaced in the longitudinal direction of the sleeve. Additional slits can be provided to reduce the spring hardness. Particularly preferably, two slits extend in different, preferably opposite directions. In the case of a sleeve having a single slit, there is a tendency for the sleeve to bend to one side when loaded. The sleeve can be stabilized against bending by providing a plurality of slits which extend in different directions. It is particularly advantageous when two slits extend in opposite directions i.e. the sleeve has slits on radially opposite sides, which are interspaced in the longitudinal direction of the sleeve. The slits themselves are therefore not situated opposite one another. The directions of the slits, namely toward the base of the slits, are opposite, however.

Preferably, the distance between adjacent slits as measured from slit edge to slit edge is at least one-tenth of the outer diameter of the sleeve, in particular at least one-seventh of the outer diameter of the sleeve.

The sleeve is preferably inserted onto the supply lead. This permits simple, rapid installation. Particularly preferably the sleeve is crimped with the supply lead. An electrical connection that is suitable for transferring high currents can be created easily in this manner.

The sleeve can be inserted onto the glow element. Preferably, however, the sleeve is inserted onto an intermediate piece situated between the glow element and the sleeve. Advantageously, the intermediate piece can bring about an adaptation between the diameter of the sleeve and that of the glow element.

Further details and advantages of the invention are explained using an embodiment, with reference to the attached drawings. In the drawings:

A glow plug according to the invention preferably has a ceramic glow element, although it can also have a glow element composed of metal, in particular steel. The advantage of simple length compensation by a contact spring according to the invention is particularly significant for ceramic glow elements, however, since they are fragile.

FIG. 1 shows an embodiment of a glow plug according to the invention;

FIG. 2 shows a sectional view of FIG. 1; and

FIG. 3 shows the contact spring of the embodiment shown.

The glow plug shown in FIG. 1 has a housing 1, out of the front end of which a ceramic glow element 2 extends. A potential connection 3 is disposed on the rear end of the glow plug, via which glow element 2 can be connected to a voltage source. Housing 1 is used as the ground connection.

FIG. 2 shows a sectional view of the rear part of the glow plug shown in FIG. 1. A supply lead 4 which is connected to glow element 2 via a contact spring extends away from potential connection 3 in housing 1. Contact spring 5 is shown in FIG. 3 and is designed as a metal sleeve which comprises a plurality of slits 6 extending transversely to the longitudinal direction thereof. Preferably exactly two slits 6 are provided, as is the case in the embodiment shown.

Slits 6 are separated by a distance in the longitudinal direction of cylindrical sleeve 5. Slits 6 extend in opposite directions i.e. in FIG. 2 one of the slits 6 extends from left to right and the other slit 6 extends from right to left. The width of slits 6 determines the maximum range of spring by which the spring can be compressed in the longitudinal direction. Preferably slits 6 have a width that is greater than the wall thickness of sleeve 5. A slit width in particular that is between one-tenth and one-fourth of the outer diameter of the sleeve is advantageous. In the embodiment shown, the slit width is one-fifth of the outer diameter of sleeve 5.

The distance between the two slits 6, as measured from slit edge to slit edge, is preferably at least one-tenth of the outer diameter of sleeve 5. Distances in particular of between one-seventh and one-fourth of the outer diameter of the sleeve are advantageous. Furthermore, it is preferable for the distance between the two slits 6 to be between one-half and twice the slit width. The distance and the slit width are approximately equal in the embodiment shown.

Slits 6 preferably extend perpendicularly to the longitudinal direction of sleeve 5, although they can basically also extend obliquely to the longitudinal direction. Slits 6 are located in a cylindrical section of sleeve 5 and have a depth that is preferably between one-tenth and one-fifth, in particular between one-seventh and one-fifth of the outer diameter of the cylindrical sleeve section. Preferably sleeve 5 has a consistent diameter along the entire length thereof, as is the case with the embodiment shown. Sleeve 5 can have another diameter, however, on one of the ends thereof in particular e.g. to simplify insertion onto supply lead 3, glow element 2, or other parts.

Sleeve 5 is inserted via one end onto supply lead 3 and is crimped therewith. Sleeve 5 is placed via the other end thereof onto an intermediate piece 7 disposed between sleeve 5 and glow element 2. Intermediate piece 7 is preferably inserted onto glow element 2.

The glow plug that is depicted is a pressure-measuring glow plug. Glow element 2 can be moved against a return force in the longitudinal direction thereof relative to housing 1. The position of glow element 2 relative to housing 1 is detected using a sensor, which is not depicted, and the combustion chamber pressure is determined on the basis thereof.

REFERENCE NUMERALS

1 Housing

2 Glow element

3 Potential connection

4 Supply lead

5 Contact spring

6 Slit

7 Intermediate piece 

1. A glow plug comprising a housing (1), a glow element (2) that extends out of the housing (1), a supply lead (4) which is enclosed by the housing (1) and is connected via a contact spring (3) to the glow element (2), characterized in that the contact spring (5) is a sleeve having at least one slit (6) extending transversely to the longitudinal direction of the sleeve.
 2. The glow plug according to claim 1, characterized in that the slit (6) extends perpendicularly to the longitudinal direction of the sleeve.
 3. The glow plug according to one of the preceding claims, characterized in that the slit (6) has a depth that is more than one-half, preferably more than two-thirds, in particular more than three-fourths of the outer diameter of the sleeve (5).
 4. The glow plug according to claim 3, characterized in that the depth of the slit (6) is between one-tenth and one-fifth of the outer diameter of the sleeve (5).
 5. The glow plug according to one of the preceding claims, characterized in that the slit (6) has a depth that is between one-tenth and one-fourth of the outer diameter of the sleeve (5).
 6. The glow plug according to one of the preceding claims, characterized in that at least two slits (6) are provided which are interspaced in the longitudinal direction of the sleeve (5) and extend in different, preferably opposite directions.
 7. The glow plug according to claim 6, characterized in that the distance between adjacent slits (6), measured from slit edge to slit edge, is at least one-tenth of the outer diameter of the sleeve.
 8. The glow plug according to one of the preceding claims, characterized in that the sleeve is inserted onto the supply lead (4).
 9. The glow plug according to one of the preceding claims, characterized in that the sleeve is crimped with the supply lead (4).
 10. The glow plug according to one of the preceding claims, characterized in that the sleeve is inserted onto an intermediate piece (7) situated between the glow element (2) and the sleeve. 